The transcription factor AFosB accumulates in specific regions of the brain in response to chronic chemical and electrical insult. The accumulation of AFosB in response to chronic drugs of abuse, first generation anti- psychotics and anti-depressants, L-DOPA, electro-convulsive seizures, as well as conditions such as Parkinsons and epilepsy, is thought to regulate gene expression, mediating long-term neurological and behavioral changes such as drug seeking behavior and dyskinesias. While a number of studies have characterized the expression profile of genes altered by AFosB accumulation, little is known about the functional molecular entity of AFosB in vivo. In particular, while AFosB, a basic leucine zipper (bZIP) protein, has been suggested to form a functional transcription factor as a heterodimer with JunD (on AP-1 DNA consensus sequences on the promoter regions of target genes such as cyclin-dependent kinase 5 (cdk5)), no jun accumulation can be detected in parallel with AFosB upon chronic stimulation. Importantly, although AFosB readily forms homodimers and binds AP-1 sites in a specific manner in vitro, it is unknown if such homodimers could form functional transcription factors in vivo. To address this controversy we propose to: Aim 1. Identify small molecule compounds that inhibit the ability of the AFosB homodimer to bind to the AP-1 site in the promoter region of Cdk5. Aim 2. Identify small molecule compounds that inhibit the ability of the AFosB/JunD heterodimer to bind to an AP-1 consensus sequence. Aim 3. Test the ability of the small molecule compounds identified to disrupt the binding of AFosB to target genes in ceil culture as well as in vivo (brain tissue). The research design employs a chemical approach to develop tools that differentiate between different AFosB species in vivo though their specific inhibition. In the future, these tools will permit the gene expression profiles of different functional species of AFosB to be characterized as a function of chronic insult.. Understanding the molecular characteristics of AFosB in its active form(s) may reveal new therapeutic approaches to prevent adverse neurological and behaviroral changes that accompany chronic drug use, as well the dysinesias that accompanies use of L-DOPA and first-generation anti-psychotic drugs.